1. Field of the Invention
This invention relates to item counting or detecting apparatus. Although it is generally applicable to all types of item counting or detecting apparatus, it is especially applicable to the counting of printed articles, such as newspapers, magazines, or the like which are conveyed in either overlapped condition or singly past a counting station.
2. Description of the Prior Art
Heretofore, counters for the above purpose were generally of the mechanical type wherein the leading edges of printed articles being counted engage mechanical sensors to cause counting. Such mechanical systems, however, tend to introduce errors in counting due to irregularities in the printed articles, variations in thickness of the articles, inertia and vibration of the counter actuator, particularly when operating under high speed, etc.
Accordingly, attempts have been made to utilize electro-optical counting devices for the above purpose but these have also encountered problems which often result in incorrect counting. One of the most successful electro-optical counters is that disclosed in the U.S. Pat. No. 4,217,491 issued to M. H. Dufford, Jr. et al on Aug. 12, 1980. In such system, a continuously modulated beam of light is directed toward the path of the items being counted and the optical energy being reflected from the items is sensed by two separate light sensors arranged at an angle to each other and to the modulated beam. The reflected energy detected by the sensors is integrated over a relatively large number of oscillations and the resulting gains are compared and when a sufficient differentiation in signal strength is reached, a counter is actuated. However, as the surface of each item is scanned, cross-modulation tends to occur due to changes in reflectivity of the item surface, i.e changes in color print density, surface texture, thickness of the item, etc. This tends to cause erroneous actuation of the counter.